1. Field of the Invention
The present invention relates to a hot isostatic pressing device.
2. Description of the Related Art
An HIP process (a pressing method using a hot isostatic pressing device) for treating a workpiece such as a sintered product (ceramics, etc.) or cast product at a high temperature equal to or higher than recrystallization temperature thereof under a high-pressure pressure medium gas atmosphere of several tens to several hundreds MPa is characterized by that residual pores in the workpiece can be extinguished. Therefore, this HIP process is confirmed to have effects such as improvement in mechanical characteristics, reduction in dispersion of characteristics, and improvement in yield, and thus has come to be extensively used for industrial purposes.
Now, in the actual industrial production site, speeding-up of the treatment is strongly desired, and it is essentially required for this to perform a cooling step that takes the longest time particularly among the steps of the HIP process in a short time. Therefore, with respect to conventional hot isostatic pressing devices (hereinafter referred to as HIP devices), various techniques are proposed to improve the cooling rate while maintaining the inside of a furnace in a thermally uniform condition.
For example, Japanese Examined Utility Model Application Publication No. 3-34638 discloses an HIP device in which the inside of a high-pressure container for storing a workpiece is divided into two chambers by providing a heat insulating layer and a casing inside the high-pressure container, and the inside that is isolated thermally and air-tightly by the heat-insulating layer and the casing is defined as a hot zone (furnace chamber) for performing isostatic pressing treatment. A fan for agitation of furnace chamber internal gas and a fan for forced circulation of cooling gas are provided for the inside and outside of the hot zone respectively, so that pressure medium gas can be circulated individually inside and outside the hot zone. Since the pressure medium gases circulating respectively inside and outside the hot zone can be mutually heat-exchanged through the casing, the hot zone can be efficiently cooled by transferring the heat within the hot zone to the casing by the inside circulating flow, and then discharging it out of the high-pressure container through a container wall thereof by the outside circulating flow from the casing.
On the other hand, U.S. Pat. No. 6,514,066 discloses an HIP device including a heat-insulating layer provided inside a high-pressure container, similarly to Japanese Examined Utility Model Application Publication No. 3-34648. The HIP device of U.S. Pat. No. 6,514,066 is differed from that of Japanese Examined Utility Model Application Publication No. 3-34638 in that this HIP device is provided with three ejectors for supplying the pressure medium gas. Namely, the first ejector of the three ejectors sends pressure medium gas which is cooled by circulating outside the heat insulating layer to the second ejector, and the third ejector sends pressure medium gas higher in temperature than that in the first ejector that circulates outside the heat insulating layer to the second ejector. The second ejector mixes the pressure medium gases with different temperatures sent from the first and third ejectors together, and directly supplies the resulting pressure medium gas which is temperature-adjusted by the mixing into the hot zone, whereby the hot zone is efficiently cooled.
The HIP device of Japanese Examined Utility Model Application Publication No. 3-34638 has a structure capable of easily maintaining the hot zone in a thermally uniform condition since the hot zone is isolated thermally and air-tightly by the heat insulating layer and the casing. However, this device has a limitation in enhancement of cooling efficiency since the heat-insulating layer inhibits the heat within the hot zone from moving out of the high-pressure container when cooling the hot zone. Particularly, when the temperature in the hot zone drops to about 300° C., the cooling efficiency can be seriously deteriorated, resulting in a prolonged cooling time.
On the other hand, the HIP device of U.S. Pat. No. 6,514,066 can maintain high cooling efficiency since the cooled pressure medium is directly supplied to the hot zone, differed from that of Japanese Examined Utility Model Application Publication No. 3-34638, and also can maintain the hot zone in a thermally uniform condition since the temperature of pressure medium gas to be supplied to the hot zone can be adjusted by the second ejector. In this HIP device, however, it can hardly be expected to enhance the flow of pressure medium gas circulating outside the heat insulating layer by the intake air by the first ejector since the intake port of the first ejector is provided in a position distant from the flow of pressure medium gas circulating outside the heat insulating layer. Namely, the flow rate of the pressure medium gas circulating outside the heat insulating layer cannot be raised much since this pressure medium gas merely circulates by natural convection. Therefore, it takes a lot of time to transfer the heat in the hot zone to the high-pressure container, and it is impossible to maximize the cooling effect.